Mach 5.1

[Mac1337]

http://gizmodo.com/watch-boeings-x-51a-waverider-scramjet-blast-off-to-ma-490575939

NASA's X-43, also a scramjet drone, tops out at 7,000 mph.

[Will Collier]

Nice accomplishment. The hypersonic regime is very tricky, particularly for controlled flight with an air-breathing engine. The gas constant becomes variable, O^2 breaks up into single-atom atomic oxygen... lots of weird stuff.

[cbelt3]

Woo hoo !!!!!

[space-time]

Will Collier wrote:
Nice accomplishment. The hypersonic regime is very tricky, particularly for controlled flight with an air-breathing engine. The gas constant becomes variable, O^2 breaks up into single-atom atomic oxygen... lots of weird stuff.

you mean this gas constant?

[Will Collier]

space-time wrote:
[quote=Will Collier]
Nice accomplishment. The hypersonic regime is very tricky, particularly for controlled flight with an air-breathing engine. The gas constant becomes variable, O^2 breaks up into single-atom atomic oxygen... lots of weird stuff.

you mean this gas constant?
Nope, the adiabatic gas constant (gamma). For up to about Mach 4, it's a constant at 1.4. Get towards Mach 5 and above and it becomes variable.

And then there are the entropy changes across the shock wave and nasty viscous flow effects, and...